Toothpastes typically contain the following general types of ingredients: a polishing agent or abrasive, humectant, binder or thickener, surfactant, and water. The humectant and water are also referred to collectively as the vehicle. In addition, agents that provide therapeutic or cosmetic benefits may be incorporated such as preservatives, fluorides, flavoring agents, sweeteners and tartar control agents. Toothpaste formulations may vary widely in the specific types of ingredients and the amounts of these ingredients that are employed. Very broadly toothpastes contain 0.1 to 8% (weight percent) binder also frequently termed thickener or gelling agent, 5 to 70% water, 2 to 70% humectant, 5 to 50 weight percent polishing agent, 0.2 to 20% surfactant and 0.1 to 25% other ingredients or adjuvants such as flavoring, sweetening, fluorides, anti-tartars, preservatives, anti-calculus agents and other therapeutic actives compatible with toothpastes.
For consumer satisfaction, toothpaste formulations should possess certain excellent physical properties to which the consumer is accustomed. These properties provide a toothpaste that has appealing taste, has good cleansing effect, is easy to rinse, has excellent mouth feel, and has physical stability. Toothpastes with acceptable physical stability do not readily harden on the shelf and do not exhibit phase separation such as water or flavor separation. The appearance of the paste as it comes out of the dispenser is also considered important. It should appear smooth and have a pleasant sheen or glossy appearance.
Carrageenan is known to be an effective binder for providing toothpaste formulations with the aforementioned desirable properties. The carrageenans form gels that are thixotropic. Such gels are reported to exhibit excellent extrudability, flavor release and rinsability. The use of kappa and iota carrageenan as binders in gel toothpaste is known to also provide a toothpaste that is non-stringy.
The generic term carrageenan is applied to dozens of similar polysaccharides derived from seaweed. All carrageenans contain repeating galactose units joined by alternating .beta.1.fwdarw.3 and .alpha.1.fwdarw.4 glycosidic linkages and are partially sulfated. The types of carrageenans may be distinguished, in part, by their degree of sulfation. Kappa carrageenan has a repeating unit of D-galactose-4-sulfate-3,6-anhydro-D-galactose providing a sulfate ester content of about 18 to 25%. Iota carrageenan has a repeating unit of D-galactose-4-sulfate-3,6-anhydro-D-galactose-2-sulfate providing a sulfate ester content of about 25 to 34%. Lambda carrageenan has a repeating unit of D-galactose-2-sulfate-D-galactose-2,6-disulfate providing a sulfate ester content of about 30 to 40%.
Ideally, the above-mentioned excellent physical properties are provided in a toothpaste that is cost effective for the consumer. There is a continuing demand to provide toothpastes at lower cost while maintaining desirable properties. This is especially important in those parts of the world where, despite its well-established benefits in dental hygiene, toothpaste is still unaffordable. One approach to lower toothpaste cost is to seek low cost replacements for specific high cost ingredients. Carrageenan, for example, is a relatively expensive ingredient. Carrageenan can sometimes be used in lesser amounts when mixed with gums and other thickeners such as carboxymethylcellulose and xanthan. U.S. Pat. No. 4,140,757 describes replacing part of the carrageenan binder in a toothpaste formulation with a less expensive synthetic amorphous silicon dioxide thickener. In cases where part of the carrageenan is replaced with other binders, oftentimes the total binder concentration must be greater than when carrageenan is used as the sole binder.
Another approach to lower toothpaste cost is to provide toothpaste with higher water content. Generally, high water content toothpastes (or high moisture toothpastes) may be expected to be less expensive due to the low expense of water relative to the other ingredients. Water content in toothpastes have been reported to vary between 5 and 70 weight percent, but most toothpastes have a water content between about 10 and 25 weight percent.
Obtaining a high moisture toothpaste having the desired physical properties is a challenge. Relatively high water content is often associated with problems of low viscosity and/or phase separation. During storage water has a tendency to move downward and oils, such a flavorings, move upward. With high moisture toothpaste, the consumer may notice "wet cap" or flavor concentration in the tip depending on whether filled tubes were stored with the caps up or down. Separation may also adversely affect the sheen or gloss of the extruded paste.
High moisture toothpastes with carrageenan are known. The following U.S. patents describe various toothpaste formulations comprising carrageenan as a binder and a water content of greater than about 30% by weight: 4,340,583, 4,814,160, 4,826,675, 5,096,699, 5,208,009, and 5,356,615. High moisture toothpastes containing carrageenan are generally formulated with humectants that are present in greater than 20 weight percent and/or with the use of more or additional thickeners.
It is an object of this invention to develop a high moisture toothpaste with favorable physical properties comprising a toothpaste formulation where carrageenan is present in a concentration of no greater than about 0.85% and the total humectant concentration is no greater than about 15%. It is a further object to provide such a formulation that has favorable physical properties without the need for additional binder.